Until the 80s every subscriber was connected to the local telephone exchange by using a copper twin cable. From the subscribers wall socket the twin cable leads to a main distribution frame, where the individual twin cables coming from several different subscribers are connected to a thicker cable containing several wires. A set of such cables may then be connected to a cable which containing hundreds and even thousands of wires is located farther away in another main distribution frame and which leads to the telephone exchange. The subscriber lines thus form a star-like network, the cables of which are connected in the local exchange. For this reason, most cables of a telephone operator are formed by subscriber lines.
Along with the digitalisation of the telephone network, attempts have been made to extend the digital network to be as close to the subscriber as possible. This has resulted in a basic solution of the kind shown in FIG. 1. In this, the individual subscriber lines (that is, the copper twin cables) are connected with one network element functioning as an access node to the network. In the access node, an AD conversion of analog signals is performed, whereupon samples are multiplexed in a so-called subscriber multiplexer to a PCM line leading to the local exchange. For each subscriber line there is hereby a specific time slot on the trunk line. A concentrator may also be used instead of a multiplexer. On-hook/off-hook detection and loop measurements of subscriber lines are also performed in the access node.
The subscriber may have a plain old analog connection, a so-called POTS (Plain Old Telephone System) connection, whereby he may connect analog terminal equipment to a 2w subscriber line directly or by way of a piece of digital terminal equipment, such as a computer modem.
In the wake of the Internet's popularity, the need for quicker data transmission has grown, which is why there has been a strong increase lately in the number of ISDN connections. For upgrading a POTS connection to a basic speed ISDN connection relaying sound and data, an adapter card is required at the exchange end of the subscriber line and an ISDN terminal is required at the subscriber end. The basic speed connection is a so-called 2B+D including two 64 kbit/s channels B and one 9.6 kbit/s signal and control channel D. The physical transmission medium is still the same twin cable. The ISDN "modem" at the subscriber end is usually an AD converter, whereby a piece of analog terminal equipment may be connected to the modem. One channel B (the POTS channel) is hereby used for transmission of an audio frequency speech signal while the other channel B is used for data transmission. Channels B are two-way channels.
Using the same twin cable quite high data transmission rates may be achieved by using ADSL (Asymmetric Digital Subscriber Line) technology. ADSL includes three separate frequency channels on the same 2w twin cable. The lowest frequency channel transmits traditional POTS audio frequency calls. The second uplink channel transmits data at a rate of 16-500 kbit/s from the subscriber's terminal equipment over the subscriber line to the network. The third channel is a high-rate downlink channel which may be used e.g. for transmitting a film from the network to the consumer. Transmission rates may be in a range of 1.5 Mbit/s-9 Mbit/s. The subscriber needs an ADSL modem. In the prototype modem there are three connectors, one of which leads to the telephone wall socket, the second is a standard RJ-11 connector intended for analog terminal equipment and the third is an RJ45 connector of a twisted Ethernet couple to which the computer is connected. It is a great advantage of the ADSL that it uses no special adapter electronics for analog equipment, but the analog connection will work even if the ADSL modem proper does not. Due to the high frequency, the subscriber line may not be very long, so that when using a rate of 6 Mbit/s the line length may be 2.5-3 km.
FIG. 3 illustrates frequencies which may be used when using the transmission methods listed above. In a POTS connection the frequency range is 300 Hz-3.4 Khz, in an ISDN connection it is approximately 300 Hz 80 Khz. With a rate of 1.5 Mbit/s the ADSL will work at even higher frequencies and its uplink channel is in a range of 85-95 Khz, while the downlink channel is in a range of 110 -410 Khz. It is essential to notice from the figure that a traditional POTS connection, an ISDN connection, an ISDN connection where a POTS signal is transmitted on one channel, or simultaneously an ISDN and an ADSL connection or a POTS and an ADSL connection may be available to the subscriber. All this is achieved by using the traditional 2w copper cable.
FIG. 2 shows in greater detail circuits located in the access node. Physically, the access node may be located in a building or it may be a small cabinet on the street. The cabinet contains a rack including one or several frames. The frame includes plug-in units having circuit cards equipped with the necessary electric circuits. In the rear part of the frame there are backplane buses through which the plug-in units are connected electrically to one another. The individual subscriber lines leading to the access node all end at their own plug-in unit and in the subscriber line interface unit located therein, which adapts the subscriber line to the network interface. In FIG. 3 the subscriber lines of ISDN subscribers thus end in ISDN cards 21, which may contain several individual subscriber line interface units, that is, several subscriber lines end on the same card. Similarly, the lines of those who have analog connections end in subscriber line interface units performing POTS adapting on POTS cards 22.
POTS and ISDN plug-in units are connected to backplane bus 29, to which unit 210 performing the network connection is also connected. The interface to the local exchange is here a standard V5.2, and unit 210 connects the access node with the exchange over 2 Mbit/s trunk lines.
In addition, the access node also includes a test unit 211, which is connected to the network management system by way of a standard network management interface Q3. Test unit 211 is connected through a separate test bus 28 to the ISDN and POTS subscriber line interfaces 21 and 22. The test unit performs the conventional loop measurements of subscriber lines and supplies the results for use by the network management.
When subscribers find that their present POTS and ISDN connections are too slow for use on the Internet, they may require that the operator provide an ADSL connection offering a speed many times higher than the speed allowed by the ISDN connection. Such a need will occur by that time at the latest when more ADSL modems intended for the subscriber end of the subscriber line are commercially available. This is why the telecommunications operator may prepare himself for an introduction of ADSL technology by adding ADSL modems to the existing access node and by equipping new access nodes with these. FIG. 2 illustrates this situation. The figure shows a set of ADSL modems 27, to each of which a subscriber line can be connected. Besides the ADSL technology, preparations can be made for the VDSL (Very High Data Rate Digital Subscriber Line) technology or for the HDSL (High Bit Rate Digital Subscriber Line) technology using a 2 Mbit/s PCM line. Such preparation is referred to in FIG. 2 by the mark+DSL. ADSL no longer relies on 2 Mbit/s PCM lines, which is why the figure shows ADSL connections multiplexed 212 into an own transmission network based e.g. on SDH (Synchronous Digital Hierarchy).
Since a traditional POTS connection or an ISDN connection can also be relayed in an ADSL connection, the access node must be provided both with a unit splitting the POTS part and a unit splitting the ISDN part from the ADSL signal. Reference numbers 25 and 26 indicate these splitters. Splitting is simply based on low pass filtering.
FIG. 4 shows a method of connecting subscriber lines to the node in an access node according to the described state of the art. Subscriber lines SL are connected to the node in groups, which are indicated by references UNIT 1, . . . , UNIT N in the figure. A number of n 2w copper cable subscriber lines is connected to one group, in many cases 16 twin cables (n=16) are connected. Each subscriber line SL is connected to its own subscriber line interface unit, which are presented by the reference term Interface, e.g. subscriber line SL1 of group UNIT I is connected to interface unit 1 (Interface 1). It is easiest in practice that the subscriber lines of each group are of the same type, e.g. the subscriber lines of the group UNIT 1 are POTS subscriber lines, the subscriber lines of the group UNIT 3 are ISDN subscriber lines and the subscriber lines of the group UNIT N are ADSL subscriber lines. This need not necessarily be so, but interfaces of different types may be connected with each group.
Between the end of each subscriber line and the interface unit there is a test switch R, which can be a semiconductor switch or relay and which is used for connecting the subscriber line to a Test Bus or to the subscriber line interface unit. The test unit may control each test relay R individually through the test bus. The subscriber line is normally connected to the interface unit, but when the operator wishes to perform loop measurements on the concerned subscriber line, a command is given by remote control to test unit 211, whereby the test unit will control test relay R in such a way that it will connect the desired subscriber line with the test bus for the time of measurements.
It is a problem with state-of-the-art access nodes of the described kind that always when a subscriber wishes to upgrade his connection type, e.g. a POTS subscriber wishes to have an ISDN connection or an ADSL connection or an ISDN subscriber wants an ADSL connection, an electrician must visit the subscriber to do the required connections. The end of the subscriber line is thereby connected to the new interface. Another consequence of upgrading on the site is that time will pass from the subscriber's request for connection upgrade to the performance of the upgrade, in the best case days, in the worst case weeks, depending on the operator. A method of performing a POTS.fwdarw.ISDN connection on the site is described in Patent Application WO 97/01938.
The problem remains the same, even if the access node is in connection with a local exchange. When an installation job is completed, it is possible that within a short time a new visit must be paid to the access node to upgrade the connection of another subscriber. In state-of-the-art access nodes the electrician's visit is the only way to perform upgrading.
It is an objective of this invention to solve the problem presented above. It is a special objective to perform upgrading of the subscriber connection without any visit by an electrician and almost immediately after the subscriber's request for an upgrading of his connection.
The established objective is solved in the ways defined in the independent claims.